O/T-Ford F-350 Alternator

2000 F-350 with a 7.3 diesel. Truck wouldn't start yesterday. Suspected batteries. They were 7 years old. Replaced them, also the repair shop test the alternator. It was bad. New alternator and batteries, light on dash won't go out. What next? Belongs to my Son-In-Law.Thanks....

(quoted from post at 11:43:50 06/10/11) 2000 F-350 with a 7.3 diesel. Truck wouldn't start yesterday. Suspected batteries. They were 7 years old. Replaced them, also the repair shop test the alternator. It was bad. New alternator and batteries, light on dash won't go out. What next? Belongs to my Son-In-Law.Thanks....

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If the light that won't go out is an engine code, you may just need to reset the computer. Should be instructions in the owners manual?

Otherwise, I would suspect the new alternator.

Check the plug that goes into the alternator. With the key on you should have juice in both wires.Have seen a few of these blow a fuse in the under the hood fusebox. If you have juice in both wires in the regulator, and at the back of the alternator. Then have the new alternator tested to make sure it wasn"t a defect to start with. jstpa

Take another look. Betcha you're gonna find a second alternator.

Most of those heavies had two. If memory serves me, one was up on top and the other down below.

Allan

Unless it has the "ambulance"package, as someone once called it, its only going to have one alternator, second, the owners manual aint gonna tell ya nothing about resetting codes, SO to do that, disconnect BOTH batteries for an hour or so, but I dont think thats going to do any good. Check the underhood fuse for the alt. If its good, then its in the wiring or a bad alternator.

Dunno John,

Out in this country (heavy farming and heavy towing) just about all the diesels were ordered in with the ambulance charging systems.

Allan

Ive seen and been around 2000 and up Powerstorkes for years, from many areas of the country, and havent seen but 3 or 4 with dual alts. Just stating my experience.

The new alt tested good. We had them test his old one again, it tested good also. Returned the new one(remanufactured). Had the original checked at a starter repair shop down the street. It still tested good so it was reinstalled.Checked the wires at the alt. plug. 1 has 12.25 volts.It goes to the keyswitch. Wiring diagrahm shows the other wire goes back to the fuse box under the hood then over to the right fender where it hooks to a fusible link at the starter solenoid mounted there. 12.25 volts there. Fuse at the fuse box shows only shows 1 volt there. So I'm assuming without removing the fuse box, there is something with a bad or dirty connection there. There are no breaks or frayed wires to be found. Will look again tomorrow, unless someone has a better idea.

That wire with less than 1 volt that should have 12, can I cut that wire and put an inline fuse and power off the battery to see if that is the problem??

I fought this same problem with my daughter's 99 F250 last summer, having the alternator rebuilt and buying a new one from NAPA. NAPA's alt test machine showed the fresh rebuild to be bad, so on Monday I took it back to the rebuilder and he tested it proving it would put out 120 amps. He did the tests right in front of me, and laughed when I told him the NAPA alt tester story. He said "sure they want to sell you their $100+ alternators (reman in Mexico)".

With much frustration, and encouragement from the alt rebuild guy, I kept digging until I found the problem in the factory wire harness beneath the batt box on the right side fender. Either batt acid or road salt had gotten into the covered harness and got to the junction where the 2 fusable links, the big alt output wire and the one small wire that feeds back to the alt plug. The small copper wire was down to about 2 small strands and a lot of green copper dust. The voltmeter would read 12 V, but it could not carry enough current to excite the alt. Trimming all wires back to solid copper and soldering them together and taping the heck out of it made everything work correctly. I had nearly pulled the dash wiring apart trying to find the problem there.

Don't trust a good looking wire harness. I spent days trying to find the problem. Alt rebuild guy said Ford PUs have this problem somewhat commonly. An easy test to prove your wire harness is OK is to use a spare 12V headlight bulb with 2 test leads. Hook one lead from bulb to ground, and the other from bulb to the unplugged wire harness side of the alt plug with the ignition switch turned on, engine off. One of the small wires in the plug is switched by the ignition switch, the other one is a back feed from the battery (through the possibly offending wire harness). The headlight bulb limits the current to about 5 amps, so the small gauge wire is not injured. In this test I have described, both small wires (each separately) in that connector should fully light the bulb. If the bulb lights with both wires, the dashboard side of the circuit is OK, and the wire harness going to the fusable link is OK. If I had known of this test, I would have saved a lot of time and $$$.

Good Luck in finding the gremlins!

Paul in MN

Probably yes, but your best bet is to do the "headlight test" I have described in my above post.

Paul in MN